Apparatus for deslagging and degassing molten metal

ABSTRACT

Apparatus for deslagging and degassing molten metal such as steel. Molten steel is prepared in a conventional melting furnace and is tapped into a ladle. A vacuum is applied to the slag on the surface of the steel in the ladle to deslag the steel; the vacuum source may be os such large capacity that it also provides a vacuum environment for a ladle degassing system.

United States Patent Perry [45] Nov. 28, 1972 [S4] APPARATUS FORDESLAGGING AND [56] References Cited DEGASSING MOLTEN NIETAL UNITEDSTATES PATENTS [72] Inventor: Thomas E. Perry, Chagrin Falls,

hi 2,993,780 7/1961 Allard ..75/49 [73] Assignee: fkqaulgilei SteelCorporation, Cleve- A Primal), Examiner G rald Dost Attorney-Robert P.Wright et al. [22] Filed: June 25, 1971 21 Appl. No.: 156,960 [57]ABSTRACT Apparatus for deslagging and degassing molten metal RelatedApphcat'on Data such as steel. Molten steel is prepared in a conven-[62] Division of Ser. No. 841,026, July 11, 1969, tional melting furnaceand is tapped into a ladle. A 9 vacuum is applied to the slag on thesurface of the steel in the ladle to deslag the steel; the vacuum U-S.Cl. ..266/13, V o e may be OS uch large capacity that it also pro- [51]Int. Cl ..C21c 7/00 vides a vacuum environment f a ladle degassing [58]Field of Search ..75/46, 49; 266/1 R, 34 PT,

system.

1 Claim, 8 Drawing Figures more 20 4 7 26, LADLE f" .5 FUR/W705 055AA6667? L --J 9 0E G/IfJEI? CONTROL 54 LARGE CAP/907V VACUUM SOUE'CEAPPARATUS FOR DESLAGGING AND DEGASSING MOLTEN METAL CROSS REFERENCE TORELATED APPLICATION This application is a division of my co-pendingapplication Ser. No. 841,026, filed 11 July 1969 for Ap- BACKGROUND ANDBRIEF DESCRIPTION OF THE INVENTION The present invention relates toapparatus for vacuum treatment of molten metal, particularly steel, inorder to remove the slag portion which forms at the surface of themolten metal after it is prepared in a conventional melting furnace andto degas the metal.

It is known in the steel-making art to employ vacuum devices forremoving the slag from molten steel. In accordance with the presentinvention, the vacuum source may be of larger capacity than necessaryfor the deslagging operation. Thus the same vacuum source and controlsmay be used for a subsequent vacuum degassing process common in theproduction of steel.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammetric view of aprocess in accordance with the present invention.

FIG. 2 is a side elevational view of representative apparatus useful inthe system of FIG. 1.

FIG. 3 is a front elevational view taken along line 3- 3 of FIG. 2.

FIG. 4 is a sectional view taken along line 4-4 of FIG. 3.

FIG. 5 is an elevational view taken along line 5-.5 of FIG. 2.

FIG. 6 is a partial side elevational view of an alternative form ofuptake tube.

FIG. 7 is a partial sectional view of a modified form of uptake tube.

FIG. 8 is a partial sectional view of alternative apparatus useful inthe system of FIG. 1.

DETAILED DESCRIPTION Referring to FIG. 1, a ladle 20 filled with moltenmetal such as molten steel from a conventional melting furnace (notshown) is first applied to a ladle deslagger 6 for removal of the slagin the ladle. Following the slag removing operation the ladle istransported to a ladle degasser 7 in which the charge within the ladleis degassed. Both deslagging and degassing are accomplished through theuse of a large capacity vacuum source 8 coupled individually to theladle deslagger 6 and the degasser 7 by valves 8a and 8b respectively.The valves are under the control of a control mechanism 9 whichdetermines which of the'deslagger and degasser is coupled to the vacuumsource. Thus the single vacuum source 8 supplies the necessary vacuumfor removing slag and degassing the charge in these two sequentialoperations performed on molten metal in order to refine it.

FIGS. 2 to 8 show the details of representative forms of a ladledeslagger 6 useful in the system of FIG. I, The deslagger 6 includes achamber 10 coupled to the large capacity vacuum source 8 of FIG. 1 by aconduit 12 (FIG. 5) so as to create a vacuum environment within thechamber. An uptake tube 14 is coupled at one end 14a to the chamber 10,and has a second end 14b adapted to contact molten slag 16 forming alayer near the surface of molten steel 18 contained within the ladle 20.In one form of the apparatus (FIGS. 2 7), within the chamber 10 islocated a baffle 22 (FIG. 4) disposed such that molten slag 16 beingfunneled through the uptake tube 14 is deflected by the baffle 22 into aslag box 24 forming a part of the chamber 10 and located beneath thebaffle 22. In the form shown in FIG. 8, the uptake tube 14 is flared atits lower end to form an end cap 15 having substantially the samecrosssectional area as the ladle 20. The vacuum causes both the slag l6and the molten steel 18 to rise within the uptake tube 14 until the slagis caused to flow into the chamber 10 and then into the slag box 24. Abaffle 22 may also be used with this arrangement to protect the vacuumsystem. A cascade slag trap 26 is further provided between the chamber19 and its associated vacuum source 8 to prevent any slag which does notfall into the slag box 24 from entering into and interfering with theoperation of the vacuum source 8.

The chamber 10 is a generally cylindrical housing formed in threesections and fabricated from a relatively heat-resistant andhigh-strength material, e.g., steel. Thusfthe chamber 10.comprisesopen-ended cylindrical wall portion 28, tapered outwardly toward itslower portion when disposed in an upright position so that slag enteringthe chamber 10 near its top will not stick to the walls of the chamber;a cover portion 30 of generally circular shape and concave in thedirection of the interior of the chamber 10; and the slag box 24 whichforms the lower end of the chamber 10. Cooperating annular flanges 28aand 30a, located on the peripheries of wall portion 28 and cover portion30, respectively, provide a means for bolting together the wall portion28 and the cover portion 30. Similarly, cooperatiappVuaVa Smpfifi Wiiaaand 28b, located on the peripheries of the slag box 24 and the wallportion 28, respectively, are arranged so that the slag box 24 may bereadily and detachably secured to the wall portion 28 of-the chamber 10at its lower extremity (which will be described in more detail below).Vacuum from the vacuum source 8 is introduced into the chamber 10 bymeans of an annular pipe 32 which enters the chamber 10 near the upperextremity of the wall portion 28.

Diametrically opposite the pipe 32 which permits the vacuum to beintroduced within the chamber 10 is an aperture 33 in the wall portion28 communicating with the uptake tube 1.4. The uptake tube is employedto funnel slag 16 from the ladle 20 to the chamber 10. The uptake tubemay be formed in two sections, a short section 14a permanently securedto the chamber 10 and disposed about the aperture 33 in the wall portion28, and a longer section 1412 designed to penetrate into the molten slagl6 and which is readily removable from the short section Ma so that theapparatus may be easily relocated, or repaired. In addition, difierentlengths of the longer sections may be used with various sizes of ladles.It should be noted that the uptake tube 14 is preferably substantiallystraight, as if the tube should be bent or goose-necked, the molten slag16 passing at high speed through the tube will tend to rapidlydisintegrate the wall of the tube at the point of curvature.

Preferably also, the short section 14a of the uptake tube 14 flaresoutwardly toward the aperture 33 so that the velocity of the slag 16passing through the uptake tube decreases and the baffle 22 erodes lessrapidly.

The uptake tube 14 shown in FIGS. 2 and 4 is comprised of an inner wall14d and an outer wall 14c and is beveled outwardly at its lower end. Theouter wall 14c is fabricated from a material capable of withstanding thehigh temperature of the molten material being funneled therethrough,e.g., preferably steel tube, but may also be graphite, a ceramicmaterial, or the like, and is permanent in nature. The inner wallportion 14d is fabricated from multiple layers of char-resistant paperand is adapted to be disposed within and secured to the outer wall 14cto insulate the uptake tube- 1 8 and to prevent the uptake tube 14 fromcollapsing upon evacuation under high temperature. The inner wall istemporary in nature. In more detail, the char-resistant inner wall 14dcomprises a preformed lining fabricated from a spirally wound strip ofthermally insulating paper, e.g., Kraft paper, layers of paperinterleaved with layers of asbestos, or other impregnated paper orpaper-like material. The inner wall 14d is designed to have only a shortlike, i.e., about five minutes or a long enough period to funnel all theslag l6from the ladle of molten steel, and to be-readily removable andreplaceable. The inner wall 14d should be approximately one-half inch inthickness, which is adequate to withstand the flow of slag for the timenecessary to funnel the slag 16 from the ladle 20 to the chamber 10. Theinner wall is disposed within the outer wall 14c throughout the entirelength of the outer wall 140 from end 14a to end 14b and is held inplace only at its bottom end by refractory cement or other suitableadhesive. An additional wall portion 14c may be disposed about andsecured to the outer wall portion 140 near the end portion 14b of theuptake tube 14 which penetrates the slag 16 contained within the ladle29. This additional wall portion 14a may also be fabricated frommultiple layers of thermally-insulating paper or other suitable materialbut need only cover the outer wall 140 for a distance from the end 14bof the uptake tube 14 sufficient to protect the tube against directcontact with the slag, i.e., about 12 to 14 inches, the usual depth ofthe slag 16. The inner wall 14d and the additional wall portion He maybe fabricated in one piece, being connected at their lower ends by paperconnecting piece 14f which also serves the function of protecting theouter wall 140 from deterioration. If the inner wall 14d and the wallportion 14c are not constructed integrally, the lower portion of theouter wall 140 should be protected by a suitable adhesive or the like.

Alternatively, the long section 14b of the uptake tube 14 may terminatein a cylindrical cup 17 located at the lower end of the tube and adaptedto be disposed within the molten slag 16, as shown in FIG. '7. The cup17 may be fabricated from thermally insulating paper, e.g., of the typeused for inner wall 14d, or additional wall portion Me and is intendedto be discarded after removing the slag from one ladle of molten metal.The

purpose of the cup 17 is to provide a smoother (less turbulent) entranceof the slag 16 into the uptake tube 14.

Located near the end 14b of the uptake tube 14 which penetrates into theslag 16 is a probe 34 for determin proximity of the uptake tube 14 tothe steelslag interface. The probe 34 is coupled to an electrical source(not shown) and reliesupon the difference in conductivity of the moltensteel 18 and the slag 16 to signal when the probe, which is disposedapproximately one-fourth inch belowthe end 14b of the uptake. tube 14,has contacted the molten steel 18. Thus a predetermined amount of theslag may be removed without removing any of the molten steel.

As the uptake tube 14 is preferably stationary relative to the chamber10, and the deslagging apparatus desirably remains fixed in oneposition, it becomes necessary that the ladle 20 be transported andraised until the slag portion 16 contained within the ladle 20 contactsthe end 14b of the uptake tube 14. An operator may easily position theladle 20 by means of positioning arms 36 that movably support the ladle.The operator may manipulate the ladle 20 such that the uptake tube 14contacts the slag 16 uniformly about the surface of the molten liquid,i.e., such as a vacuum cleaner is moved about a floor being. cleaned. Inorder to bring the molten slag 16 closer to the open upper end of theladle 20, the ladle may be tilted before the vacuum is applied by meansof the uptake tube 14. Depending upon the viscosity of the slag layer,movement of the ladle may not be necessary. It should be understood,however, that the deslagging apparatus may also be moved into contactwith the ladle 20. It is ordinarily easier for the operator to positionthe ladle with respect to the deslagging apparatus as part of the ladlemovement from the furnace in which the steel is prepared to the ladledegassing station, which is normally a part of the process for producinghigh quality steel.

Disposed within the chamber 10 is the baffle 22, which is suspended fromthe cover portion 30 in a position directly opposite the aperture 33communicating with the uptake tube 14. Thus the baffle 22 may deflectslag which has been rapidly funneled by the uptake tube 14 into thechamber 10 from a path which would permit the slag to enter the pipe 32,which is disposed diametrically opposite the aperture 33 and whichconnects the vacuum source 8 to the chamber. As the baffle 22 isdirectly in the path of rapidly moving, high temperature slag, it isnecessary to reinforce the bafile with a suitable member 38, e.g., aremovable steel member or refractory material, to lengthen the life ofthe baffle. Although the reinforcement member 38 is not necessary to theoperation of the deslagging apparatus just described, it is moreeconomic to utilize a replaceable massive block on the baffle 22 than tomake the baffle 22 massive itself. The baffle 22 should not be disposedtoo close to the aperture 13 as the rapidly moving slag will cause thebaffle to disintegrate too quickly.

Another method of preventing the rapidly moving slag from striking thebaffle 22 at too fast a rate is illustrated in FIG. 6. A stream of gas,e.g., inert nitrogen gas or air, may be introduced transversely to theflowing molten slag by means of a pipe w and a valve 21 connecting asource of inert gas or air or both (not shown) to the short section Maof the uptake tube 14 at a point close to the aperture 33 of the chamber10. The inert gas or air deflects the molten slag 16 from its path oftravel to prevent the slag from impinging too vigorously against thebaffle 22. The inert gas or air is preferably introduced into the pipe19 at a pressure of about 20 p.s.1.g.

In a modified form of apparatus, the long section 14b of the uptake tube14 terminates in a flared substantially cylindrical end cap 15, as shownin FIG. 8. The end cap 15 of the modified form is comprised of an outerwall 15a fabricated from the same material as the uptake tube 14 and aninner wall ISb fabricated from thermally insulating material, e.g.,thermally insulating paper such as that used to form inner wall 14d oradditional wall portion Me, or, preferably, a refractory material.

The end cap 15 has substantially the same cross-sectional area as theladle and is just able to be disposed within the ladle. The end cap ispartially immersed within the molten material. The pressure acting onthe portion of the molten slag and metal outside the perimeter of theend cap 15 is counterbalanced by the weight of a vertical column ofmetal of unit cross-sectional area and of a height the same as thedifference in levels between the slag outside the end cap and the upperend of the uptake tube (designated d in FIG. 8) plus the pressure withinthe chamber 10. Both the slag 16 and molten metal 18 are allowed to risewithin the uptake tube 14. By carefully controlling the vacuum levelproduced by the vacuum source 8, only the slag will be drawn off the topof the uptake tube 14 and will enter the chamber 10.

That is, the pressure difference between the chamber and the surface ofthe slag layer outside the end cap 15 is controlled (by regulation ofthe vacuum source 8) so that it is sufficient to support a columnfilling the uptake 14 of slag alone or molten metal and slag but notmolten metal alone. In this way the pressure difference forces slag(floating at the top of molten metal) upwardly and outwardly through theuptake tube into the chamber until all slag within the end cap has beenremoved. At this point the uptake tube is filled with molten metal and asmall amount of slag at the upper end. The vacuum may be controlled sothat the pressure difierence is not great enough to support any moremolten metal in the uptake tube, and hence the movement of moltenmaterial out the uptake tube ceases. ln this way all the slag but nomolten metal is forced out the uptake tube. The vacuum within thechamber may be varied during this operation so as to provide a rapidflow of slag initially (higher vacuum) followed by a slowing of slagflow (lower vacuum) toward the end of the operation to ensure that nomolten metal is withdrawn into the chamber.

Preferably, the ladle 20 is raised relative to the uptake tube 14 as themolten slag is removed. The end cap 15 may be disengaged from the moltenmetal in the ladle 20 when any of the molten metal begins to flow intothe chamber 10, thus breaking the vacuum and allowing the remainingmolten metal in the uptake tube 14 to run back into the ladle 20. Thereis no necessity for the receptacle for the slag to be disposed at alevel beneath that of the ladle 20. The present apparatus does notutilize the same principles as a vacuum-initiated siphon, since in theinstant device the vacuum is continuously in operation.

comprising a part of the chamber 10 and located beneath the baffle 22.The slag box 24 is adapted to be readily removed from the chamber 10upon its being filled. To this end, a plurality of wing-nut-and-boltmechanisms 40 are employed to secure the slag box 24 to the lowerperiphery of the wall portion 28 of the chamber 10 at the correspondingannular flanges 24a and 28b. The slag box 24 may be transported awayfrom and into its position in the deslagging apparatus by a transfercrane 41, for example. As the slag box 24 is adapted to contain moltenslag 16, it should be lined with refractory brick 42 or other suitablematerial, although by the time the'slag 16 is received within the slagbox 24, the slag has substantially decreased in temperature.

While the slag box 24 receives the great proportion of theslag 16removed from the ladle 20, some of the slag, particularly gaseous andfinely divided solid matter, may manage to elude the slag box 24 andfind its way to the pipe 32 which connects the vacuum source 8 to thechamber 10. To prevent this portion of the slag from subsequentlyentering into and interfering with the operation of the vacuum source 8,the cascade slag trap 26 is provided to collect this slag. The cascadeslag trap 26 comprises a series of vertical pipes 42 and 44 having theirlower end portions sealed with caps 46 and 48 designed to catch theportion of the slag which settles in the pipes. In operation (as bestseen in FIG. 5), the gaseous and finely divided solid matter of the slagenters the pipe 32, which has a horizontal portion 321; leading to thecascade slag trap 26 and a downwardly directed open-ended verticalportion 32b disposed within the first vertical pipe 42 of the cascadeslag trap. Substantially all of the slag matter existing from the openend of the vertical'portion 32b of the connecting pipe 32 settles on thecap 46 at the base of the vertical pipe 42. However, some of the slagmatter may manage to rise within the pipe 42 and enter the second pipe44 of the cascade slag trap 26 at the point of connection of the pipes42 and 44 near their upper ends. Again substantially all the remainingslag matter will settle on the cap 48 at the bottom of the second pipe44. Extending from the central region of the second pipe 44 is ahorizontal pipe 59 which leads directly to the vacuum source 8 through aflexible connector 52 and a valve 54. The valve 54 corresponds to thevalve 3a shown in FIG. 1. In this case, the valve 54 is manuallycontrolled. Although a cascade slag trap 26 containing two verticalpipes 42 and 44 is illustrated, it should be understood that one pipemay be sufficient to settle a substantial portion of the slag matter. Aplurality of pipes will increase the efficiency of the system while nothindering the maintaining of the vacuum. Thus a tortuous path isprovided to collect the portion of the slag not received by the slag box24 before it can enter into and interfere with the operation of thevacuum source 8.

The entire deslagging apparatus may be supported by a pair of flanges60, 62 located on the wall portion 28 of the chamber 10 which rest upona pair of horizontal high-strength l-beams 56, 58.

The vacuum source 8 is preferably of larger capacity than necessary foradequately deslagging the molten steel 18. If the vacuum source 8 is ofsufficiently large capacity, it may be used to provide a vacuumenvironment for the ladle vacuum degassing system; Common controls mayalso be utilized to determine the application of vacuum, as'shown anddescribed above in connection with FIG. L'Thus both the slag portion 16and the gaseous matter contained within the molten steel may be removedfrom the steel while the steel remains within the ladle 20. It isfurther desirable that the vacuum source 8 be of greater than adequatecapacity so that a high vacuum may be placed in communication with thechamber 10 when such is desired, rather than having to reduce thepressure gradually. It should be noted that when a probe 34 is employed,a thin layer of slag will remain upon completion of the deslaggingprocess; this is desirable as it provides temporary protection of themolten steel 18 during the time that the ladle 20 is being moved fromthe deslagging station to the degassing station.

The apparatus shown in FIGS. 2 f 7 allows for intermittent operationnear the end of the deslagging cycle,

which is helpful in removing the slag 16. As the end point of slagremoval is reached, the coupling together of slag and uptake tube isdiscontinued to prevent sucking molten steel into the chamber 10. Thelost remnants of slag are then sucked into the chamber with intermittentcoupling of uptake tube and slag. Such intermittent operation is notpossible with the alternative arrangement, since once the tube and slagare decoupled no more sucking can take place.

Thus, the present invention provides apparatus for deslagging moltenmetal by removing the slag from the ladle by means of a high vacuum andalso for degassing the metal. A vacuum source is employed, which isindividually connected to one of the deslagging and degassing means bymeans of a valving mechanism.

I claim:

1. Apparatus for deslagging and degassing molten metal, comprising:

a. a vacuum source;

b. deslagging means;

0. degassing means; and

d. means connecting said vacuum source individually to said deslaggingand degassing means, including valve means for coupling said vacuumsource to only one of said deslagging and degassing means at any time. 7

1. Apparatus for deslagging and degassing molten metal, comprising: a. avacuum source; b. deslagging means; c. degassing means; and d. meansconnecting said vacuum source individually to said deslagging anddegassing means, including valve means for coupling said vacuum sourceto only one of said deslagging and degassing means at any time.